Comapring a record in table with other records in same table

Hi,
We want to compare one record in a table with other remaing records of the table that meet a criteria of a business logic.

eg.I have startcall_time,end_calltime as fields with other 50 fields.
As a business logic we need to subtract start_calltime of new record from end_calltime of previous record and do some calculations.These calculations have to be done for all the calls where endcalltime(of a record)-startcall(timeof a different record )meet a criteria.

A procedure in MS SQl is what we need to write.

Please help .

Regards
AJ

DDL would help, but you could try this as a vague starting point:
select ... from yourtable t1 join yourtable t2 on (t1.field-t2.field=criteria and t1.id<>t2.id)
You are joining the table with itself, on your criteria.

tim